(a) Field of the Invention
The present invention relates to an electrostatic ink jet recording device and, more particularly, to an electrostatic ink jet recording device including a recording head for ejecting ink containing electrified toner particles.
(b) Description of the Related Art
A non-impact recording technique has drawn attention due to its small noise during a recording operation. Among other non-impact recording techniques, an electrostatic ink jet recording technique is superior because it can record images directly on a recording sheet at a high speed with a simple mechanism. Various devices have been proposed for implementing the electrostatic ink jet recording technique.
JP-A-4(1996)-80037 proposes an ink jet recording device, as shown in FIG. 1, wherein the entire spacing area 34 in which a recording head 31 in the recording device 30 moves in the transverse direction of a recording sheet 35 is divided into three areas including a printing area 32 and a pair of non-printing areas 33 disposed at both sides of the printing area 32. The recording head 31 has a plurality of ink ejection nozzles aligned in the transverse direction of the recording sheet for ejection of the ink.
FIG. 2 schematically shows the longitudinal section of the nozzle surface of the recording head 31, wherein the plurality of ink ejection nozzles 41 are aligned, for showing the situation of the individual ink ejection nozzles 41 when the recording head resides in the printing area 32 and the non-printing areas 33.
In FIG. 2, "ON" and "OFF" means application of recording voltages to individual ink ejection nozzles 41. A low bias voltage is applied to all of the ink ejection nozzles 41 when the recording head 31 resides in the non-printing area 33, whereas a specified group of ink ejection nozzles 41 are driven with a higher, printing pulse train when the recording head 31 resides in the printing area 32. In this example, the printing pulse train is not applied to the two when the recording head 31 resides in the printing area 32.
FIG. 2 shows the shape of ink meniscuses 43 and 42 on the nozzle surface in the printing area 32 and the non-printing area 33. In the non-printing area 33, the nozzle surface gets wet with ink due to the application of the small bias voltage to the ink ejection nozzles 41, thereby a small ink meniscus 42 to be formed between each adjacent two of the ink ejection nozzles 41. It is stated in the publication that the small ink meniscus 42 provides an excellent ejection of ink droplets 43, the direction of which is substantially normal to the nozzle surface, when the specified ink ejection nozzles 41 are driven by the printing pulse train.
In the proposed ink jet printing device as mentioned above, although the bias voltage is below a threshold voltage for ejection of ink droplets, the bias voltage applied in the non-printing area sometimes causes an undesirable ink ejection from the ink ejection nozzles depending on the situations of the nozzle surface, that is, a lightly wet state or a heavily wet state of the nozzle surface.